The proposed research examines the effects of temperature and pressure on the phase transitions and morphology of blood platelets and their microtubules. In addition, examination of the viable life time of platelets stored under various conditions will be made with the goal of lengthening the viable storage life of blood platelet concentrates. Evidence has been presented indicating that hydrophobic bonding is largely responsible for the formation of the microtubules and the consequent sickling in sickle cell erythrocytes. This is essentially a thermodynamic process, and similar principles are likely to apply to the maintenance of the disc shape in blood platelets through the formation of microtubules. Cooling is known to disaggregate the microtubules in platelets, and platelets lose their discoidal shape assuming a more random, irregular shape with numerous pseudopods. Preliminary work has shown that the application of about 300 atm. of pressure tends to prevent this shape change on cooling. This project will examine the fundamental processes involved in their changes, including study of the microtubules, suspension of contractile protein and intact platelets under varying conditions of pressure and temperature. The feasibility of using pressure accompanied by low temperature to prolong the viable storage life of blood platelets will be examined using both in vitro and in vivo (animals) techniques. The use of some chemical substances such as PGE, and gentisic acid will be considered. Additionally, fundamental information on the effects of pressure on microtubules and hydrophobic bonding should be obtained.